I have the service model XD 40 and I purchased a 9 mm barrel for it. So, it's almost a two for one. I can shoot the inexpensive 9 mm all day.
The XD is the most comfortable handgun I have ever used! For me, and handgun fit is very individual, it points better and sits more naturally in my hand than Glocks, H&K and Sigs. They are all fine weapons, but when my son and I go to the range, we both go for the XD. I sold my Glock G26 and 36 once I had used the XD. My beautiful Kimber Custon I 1911 (45) just sits in its case.
I would like the compact XD as a carry, but it is pretty bulky compared to other compacts. The Kahr P9 (9 mm) is small and light, the PM 9 is smaller and lighter. I would not get the PM 40 because of all the problems people have had. It's just too small a gun to handle the beefy 40 S&W round. The P 9 and PM 9 will take about 200 rounds to break in because they are built with such close tolerances. A very nice compromize is the P 9 Covert. It has the slide and barrel length of the P 9 and grip of the PM 9. It's probably half the weight of the compact XD and will fit in your pocket.
Don't discount the Kel-Tec or Bersa 380 caliber. It only has 1/2 the wallop of the 9 mm, but twice the punch of the .32. A Kel-Tec P 3AT weighs in at something like 8 oz, will drop invisibly into a front pants pocket, can shoot the 380 +p at over 1000 ft/sec, and costs just over $200. If anyone whines about the 380 lack of stopping power, remember - the gun you carry has much better stopping power than the gun you left at home because it was too big or heavy.
A hammerless revolver such as the S&W 642 can be a good carry. The 642 is 38 spl and weighs about 15 oz. Before people start warning about stopping power of the 38 spl, I will tell you that the 38 spl +p (higher pressure, higher velocity) hollow point rounds are not something you want to be on the wrong end of.
After all this, I must say that carryng on a motorcycle from state to state was a PIA! Even in states with concealed carry reciprocity with my state, I had to deal with restaurants where they served alcohol and guns were therefore banned. So, I would have to move my gun from the tank bag to a locked hard case, without anyone seeing, before entering the restaurant. When I reached a state that did not have reciprocity, I had to stop near the state line, remove the ammo, put a trigger lock on the gun, and keep the gun and ammo in separate places. A PIA!
Best Wishes for your choice,
Ron